Speed correction gear for gyro compasses



Oct. 28, 1952 F. CARTER 2,615,258

SPEED CORRECTION GEAR FOR GYRO COMPASSES Filed Oct. 25, 1947 2 SHEETS-SHEET 1 INVENTOR. L554 0: FCIQRTER L. F. CARTER SPEED CORRECTION GEAR FOR GYRO COMPASSES 2 Sl-IEETS--SHEET 2 Oct. 28, 1952 Filed Oct. 25, 1947 a; M mill!!! M W 53 36'- "1 i 60 023 12 36 i l I DINVENTOR L 1 LESLIE EGQR ER 52 W H/5 ATTORNE Patented Oct. 28, 1952 SPEED CORRECTION GEAR FOR GYRQ COMPASSES Leslie F. Carter, Leonia, N. 3., assignor to The Sperry Corporation, a corporation of Delaware Application October 23, 194 7, Serial No. 781,737

- 1 This invention relates to gyroscopic compasses, and particularly to means for correcting the readings of such compasses for errors due to the speed, course and latitude of the craft in which they are carried. The principles on which these corrections are based are set forth in U. S. Letters Patent to Elmer A. Sperry, No. 1,255,480, issued February 15, 1918,. and to Harry L. Tanner, No. 1,412,760, issued April 11, 1922.

It is well known that the systematic error of a gyro compass can be expressed by the formula:

vError=A K Cos course-Xsec. latitude-I-B tan latitude. WhereA and B are constants and K stands for the speed of the ship over the sea bottom. The constant B depends on the construction of the compass and in some types of gyro compass the value of B is zero.

,One of the objects of the present invention is to provide a correction device of simpler construction and fewer parts than those hitherto known.

A second object of my invention is to eliminate linear sliding-motions in the mechanism and to relay entirely on rotary motion. This construction has two advantages since it dispenses with the necessity for accurately machining and fitting of plane sliding surfaces and eliminates backlash in the resultant motion.

A third object of the present invention is to reduce the weight of the whole compass and in particular to reduce the load to be moved by the corrector mechanism itself by eliminating moving parts which hitherto have had to be counterpoised by idle masses.

The invention also relates to the novel features or principles of the instrumentalities describedherein, whether or not such are used for the stated objects, or in the stated fields or combinations.

Other objects and advantages of the invention will appear from the appended description when read in connection with the accompanying drawings in which,

, Fig. 1 is a side view, partly in section of part of a' gyro compass with the new correction device mounted thereon;

Fig. 2 is a plan view of the correction device;--, Fig.3 shows a method of operating a transmitter fromthe correction device alternative .to the method Of Fig. 1;

Fig. 4 shows in plan an alternative form of part'of the mechanism of Fig. 2;

Fig. 5 is a sectional view of a clamping device which forms part of the invention.

3 Claims. (01. 35226) Referring now to Figure 1 it should be observed that the compass includes three separate elements which are capable of different rotations inazimuth. Firstly, there is the main frame I I, usually hung in gimbals, and changing its orientation with the ship. Secondly, the power driven compass element, commonly called the phantom,

which is rotatably mounted in the main frame and preserves its geographical orientation so that it appears to turn relatively to the frame when the'ship changes course. This element is represented in Figure 1 by thetubular member 12 carrying the compass card I3v This tubular member is fixed to the upper end of stem II2 rotatably mounted in frame II and carrying, at its lower end, the phantom ring I20. Thirdly, there is the lubber ring shown in section at I4 which carries the lubbers mark (not shown) indicating the ships courseon the card. The lubber ring is capable of rotating in azimuth on the frame I I a few degrees either side of its normal or-zero position for the purpose of introducing the correction to the indicated course in accordance with the formula above referred to.

The tubular element I2 carries a normally horizontal ring I5 pivoted on a diameter I5, I1 for rotation round a horizontal north-south axis. Ring I5 can be manually tilted through any angle from 0 to about 20 by the knurled knob I8 which drives pinion I9 and toothed wheel'20 fixed solid to ring I5. See Fig. 2.

A fork 2I rotatably mounted in sleeve 22 has downwardly projecting ends23 which rest on the upper surface of ring I5 at points "apart as shown more clearlyin Figure 2. Sleeve bearing 22 is pivoted by a pair of lugs 22' on bracket 24 which is boltedto frame member II, and a spring 25 presses fork ends 23 into contact with ring I5.

If theship is on either a north or south course, the pivots I6, ll of ring I5 will be collinear with the axis of the fork in sleeve 22 and fork 2I will have the same inclination as ring I5. If the ship is on either an east or west course, the pivots 16, ll of ring I5 will lie under the projecting ends 23 of fork 2I and will be at right angles to the axis of the sleeve 22. In that case the fork will have no tilt, whatever the inclination of ring I5. On intercardinal courses the fork will have less tilt than the ring; in fact, the inclination of the fork will be equal to the inclination of the ring multiplied by the cosine of the course. of the ring set manually is 'made equal to A K sec. latitude the inclination of the fork 2| will Hence if the inclination be equal to the first term of the formula for the correction to be applied to the compass.

In order that the cam ring [5 may be initially set by hand according to the speed and latitude of the ship, so as to give the appropriate correction to the compass readings, a chart plate 55 is provided. i

This plate is inscribed by engraving or otherwise with a number of speed curves, and is fixed above the fork 2| by mounting bracket 56 attached to the rotating element l2. A toothed wheel fixed to ring [5, engages a pinion 51 journalled in an extension of cylinder l2. The shaft of pinion 57 carries a radial arm 58 bearing a bar 59 which moves above the surface of chart plate 55 according to the inclination given to the ring l5. Bar 59 is marked with a scale of latitudes, said scale and the curves on the chart plate being so calculated that when the mark on the bar corresponding to the ships latitude is brought over the curve on the chart plate corresponding to the ships speed, the ring I5 will have the necessary inclination to generate the appropriate compass correction for those conditions.

The manner of introducing this correction to the compass reading is as follows:

Fork 21 carries a downwardly projecting arm 21 which engages the slotted end of lever 28. This lever is rotatably mounted on stud 29 projecting from bracket 24, said bracket being carried on main frame II.

A second lever 30 independently mounted on stud 29 is provided with a clamp screw 26, tapped into lever 30 andpassing through a curved slot in lever 28. This allows lever 30 to be offset by a small angle up to about 5 on either side of the line of' lever 28, and clamped solid-therewith. A mark 3| on lever 30 cooperates with a scale of latitudes engraved near the end of lever 28, and this permits the amount of offset to be adjusted in accordance with the second term of the correction formula. An upwardly projecting pin 32 mounted on lubber ring l4 engages'a radial slot 33 in lever 30 and rotates the lubber ring 14 round the central vertical axis of the compass, so introducing the total correction. to the compassreadings.

In many cases a gyrocompass is provided with a transmitter for transmitting its indication to other parts of the ship such a transmitter being conveniently driven from an azimuth gear 35 rotating with the phantom element I20. If the transmitter is carried on the main frame H the indications transmitted will not be affected by the correction mechanism andwill be in error accordingly. This difficulty has been surmounted hitherto by attaching the transmitterto the lubber ring, which causes the correction to be introduced into the transmitted readings. This is objectionable because the location of the transmitter varies with the amount of correction being applied thereby causing variations inthe balance of the whole compass in its gimbals. This objection may be got over by attaching a counterpoise to the lubber ring 180away from-the transmitter so that the common center of gravity is on the central axis of the compass. Thisidle mass however, having to be moved by the correctcr mechanism throws an' additional load thereon and makes it necessary for the mechanism to be stronger and heavier than would otherwise be the case.

In my invention I avoid these difficulties by novel means as will now be described.

Referring to Figure 1, the azimuth gear 35 drives the transmitter 36, fixed to main frame H through a differential gear 38. As shown in the drawing, said differential consists of a frame 39 attached to the under side of a toothed wheel 40 which is freely rotatable on shaft 43. Said frame carries two bevel pinions 4|. rotatably mounted on pivots in saidframe. These pinions are driven by a bevel wheel 42 on a shaft 43 passing through the center of wheel 40 and carrying a toothed wheel 44 driven by azimuth gear 35. Pinions 4| drive a second bevel Wheel 45 integral with a bevel wheel 46 which engages bevel wheel 46' of transmitter 36.

The lubber ring carries at 4'! a short section of internal toothed rack gearing with a pinion *48 which drives wheel 40, thus giving the correct direction of rotation to the transmitter. It will be observed that when the various gear ratios are properly chosen, any angular movement given to the lubber ring as a correction by the corrector mechanism will be. added algebraically to the normal rotation of the transmitter due to the azimuth gear, and corrected indication will therefore be transmitted to the subsidiary com- Pass dials.

An alternative method of introducing the correction to the transmitter is shown in Figure 3. Here the azimuth gear 35. drives toothed. wheel M which is fixed to the rotor spindle 3B of the transmitter, said spindle being extended below the transmitter body and journalled at 5| in the bracket 52 attached to frame II. The transmitter is therefore rotatable about its own spindle. The body or shell 36 of the transmitter carries a toothed wheel53 and is driven by the lubber ring rack 47, through pinion 48 in the same manner as the differential frame 39 is driven in Figure 1. Hence changes of course are signalled by rotation of rotor spindle 36' relatively to the transmitter body, while corrections are introduced by rotation of the transmitter body relatively to the rotor spindle 36.

It will be understood that the wires or electric leads 50 forming the connections to the transmitter must in this case have enough slack to allow of rotation of the body of the transmitter through a sufficient angle say about'360, to introduce the maximum correction in either direction; or, if preferred, a set. of conventional slip rings and contact brushes may be used as shown in the drawing.

Without departing from the spirit of this. my invention I may, instead of tilting the-ring l5, keep it in a horizontal plane and make it more or less eccentric. This form of canris shown in Figure 4 and comprises a circular ring or disc l5 resting on a fiat plate 60 (see Fig. 5) forming the top of thecylindrical phantom member [2 of Figure 1. Disc [5 has a diametral slot BI, and plate Bilhas an upwardly projecting pin 62, which closely fits the slot, and a knurl headed clamp screw 63 tapped into the plate. Screw 63- passes through. a rectangular blockiitl having. a fillet on-the underside which closely fits-.slot 6|; A chart 59 is engraved on the top surface of disc [5 and a bar 55 graduated according to thelatitude projects from the side of block 64. Thecam I cantherefore be adjusted and clamped to have apredetermined amountof eccentricity just as the cam ring of Figures 1 and 2 could beset to have a. predetermined amount of tilt.

The cam l5 has a grooved periphery and'turns in a sheave 69 which is hinged toe. lever 10 which takes the place-of the fork 2i and. is pivoted on stud 29. The extension of the lever beyond stud 29 takes the place of lever 28 in Figure 1 and the rest of the mechanism is as shown in that figure.

Since many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. In a meridian-seeking gyrocompass for navigable craft having its compass member including a compass card and phantom elementall universally supported on the craft and adapted to rotate about a vertical axis, said compass further including a shiftable lubber line adapted to be read against said compass card, a device for correcting the indications provided by said gyro compass comprising an inclinable cosine cam ring pivotally supported on the phantom element in coaxial relation to the vertical axis of said compass member, means for adjusting the inclination of said cam ring, said means including a chart plate calibrated in terms of craft speed and craft latitude and a cooperating settable cursor operable by said cam adjusting means, said cam ring and chart plate each being symmetrically arranged relative to said vertical axis whereby no tilting torques are imparted thereby to said compass member, a cam follower engaging said cam ring and actuated thereby and arranged to move in azimuth with said craft, the displacement of said cam follower being dependent upon the adjusted inclination of said cam ring and the craft course angle, and means operable by said cam follower for shifting said lubber line. 1

2. In a meridian seeking gyrocompass for navigable craft having its compass member including a compass card and phantom element all universally supported on the craft and adapted to rotate about a vertical axis, said compass further including a shiftable lubber line adapted to be read against said lubber line, a device for correcting the indications provided by said gyrocompass comprising an inclinable cosine cam ring pivotally supported on the phantom element in coaxial relation to the vertical axis of said compass member, means for adjusting the inclination of said cam ring, said means including a chart plate calibrated in terms of craft speed and craft latitude and a cooperating settable cursor operable by said cam adjusting means, said cam ring and chart plate each being symmetrically arranged relative to said vertical axis whereby no tilting torques are imparted thereby to said compass member, a cam follower engaging said cam ring and actuated thereby and arranged to move in azimuth with said craft, the displacement of said cam follower being dependent upon the adjusted inclination of said cam ring and the craft course angle, a first lever pivoted on the compass frame and actuated by said cam follower, a second lever pivoted coaxially with said first lever and engaging said shiftable lubber line, and means for clamping said second lever to said first lever at a predetermined angle according to the latitude, whereby to introduce the required correction to the compass readings.

3. The gyro compass of claim 1 wherein the means operable by said cam follower for shifting said lubber line includes an adjustable linkage, and means for adjusting said linkage to provide a further shift of said lubber line in accordance with the latitud of the craft.

LESLIE F. CARTER.

REFERENCES CITED The following references are of record in the file of this patent:

Great Britain Mar. 1, 1922 

